To date, a number of ceramic oxides with the perovskite structure have been proposed as membrane materials for the selective separation of oxygen and the partial oxidation of hydrocarbons due to their high oxygen permeation fluxes. In contrast, their instability under an oxygen pressure gradient and consequent lattice expansion has been shown to be the cause of their decomposition over time, thus generally limiting their use to oxidizing environments. This has led the search for possible materials to be diverted towards alternatives such as composites. In this work, we aim to further our understanding of oxygen transport in composite materials by continuing our studies on a model mixed conducting system of (YSZ) and (LSM) using the isotope exchange depth profiling method in conjunction with secondary ion mass spectrometry (SIMS). The measured effective tracer diffusion coefficients were in the range and the effective surface exchange coefficients in the range . The activation enthalpies for oxygen diffusion and surface exchange processes were calculated to be 113 and , respectively.